This invention relates to the field of electrical capacitors of the type which employ oxide dielectric materials.
The use of chemically formed dielectric materials in electrical capacitors, especially in energy storing capacitors is a well established practice which dates back to at least the 1920's era. The electrolytic capacitors used in power supply wave filtering and more recently, as signal coupling reactive elements in radio, television, computer and electronic apparatus, are notable examples of capacitors which employ chemically derived dielectric materials. Frequently, in these capacitors, a metallic electrode member is fabricated from materials such as aluminum or tantalum with an oxide of the electrode material serving as the dielectric insulator between adjacent capacitor electrodes.
As the physical size and mass associated with electronic apparatus has decreased through the vacuum tube, transistor and integrated circuit eras, a need for capacitor elements of smaller physical size and enhanced electrical performance has intensified. In recent years, the need for electronic apparatus in space equipment such as communications satellites, vehicles which deliver satellites, and other space hardware, together with the possibility of deploying defensive weaponry into space, has particularly intensified the need for improved capacitors. In the latter use group, the prospect of deploying lasers, kinetic energy weapons, and other energy delivering systems into space has particularly intensified the search for enhanced performance electrical energy storage capacitors-capacitors which are capable of rapidly delivering a store of energy accumulated over a period of time while occupying a minimal amount of physical volume and having low physical mass.
Presently, available capacitor technology is found to limit capacitor energy storing to the range of 40 joules of electrical energy per kilogram of capacitor weight or about 88 joules per pound of weight. A large factor in determining this energy per unit mass capability resides in the limiting capability of presently available capacitor dielectric materials. Especially limiting are the thermal conductivity, capacitance density, breakdown voltage, resistivity, relative permativity and dissipation factor characteristics of the available dielectric materials.
The capacitors of the present invention achieve energy storage density at a rate which is in the range of 1 megajoule per cubic foot of volume with a weight of some 440 pounds or at a rate of 2270 joules per pound of weight. This improved capacitor performance ability is achieved largely through the use of dielectric materials of enhanced electrical and physical properties such as are described in the above referenced co-pending patent document. The capacitors of such characteristics are especially envisioned for use in the space weaponry field--such as in the currently active Strategic Defense Initiative (SDI) program wherein devices of heretofore unprecedented energy delivery rate are contemplated for parking in space orbit.